1. Field of the Invention
The present invention relates to an illumination optical system and a projection display optical system which are used in a projection type image display apparatus.
2. Description of Related Art
Conventionally, in a projector type display (a projection type image display apparatus), a liquid crystal display panel or a micromirror array device panel is typically used as a light modulation element for switching to control transmission and shielding or deflection of light to project a selected light pattern onto a screen, thereby displaying an image on the screen.
In the projector which employs the liquid crystal display panel or the micromirror array device panel as the light modulation element, it is important to use light from a light source with high efficiency and reduce variations in illuminance on the screen.
An optical integrator formed of two lens arrays each including lenses arranged two-dimensionally is a known means for improvement. In the optical integrator, a first lens array splits a luminous flux from a light source into a plurality of luminous fluxes, and a second lens array enlarges the luminous fluxes and forms images by the luminous fluxes superimposed one on another on a display area of a light modulation element (see Japanese Patent Application Laid-Open No. 11(1999)-64848).
In this method, since the split luminous fluxes with small variations in illuminance are superimposed, the resulting irradiation light has high uniformity to significantly reduce variations in illuminance on the screen. When the first lens array has each aperture formed in a rectangular shape similar to the display area of the light modulation element, all the split luminous fluxes are irradiated to the display area without waste. This improves the efficiency of the irradiation light and thus improves the use efficiency of the light from the light source.
Another means for improvement is to guide light from a light source to a kaleidoscope to mix the vectors of light rays to provide uniform light intensity distribution at an end surface of the kaleidoscope from which the light emerges, and then form a conjugate image by an image-forming lens on a micromirror array device used as a light modulation element.
When the kaleidoscope is used, an optical system is complicated if a means for converting natural emission light from the light source into linearly polarized light is used. Thus, such a means is not used generally.
In the method, the resulting irradiation light has high uniformity to significantly reduce variations in illuminance on a screen.
However, in the method of providing uniform light intensity distribution using the optical integrator formed of two lens arrays or the kaleidoscope, the luminous flux illuminating the light modulation element has a large convergent angle. When the light modulation panel is realized by a reflection type liquid crystal display panel or a micromirror array device, limitations are imposed on space for forming an optical path along which the illumination light is guided. When a TIR prism is used to guide light, the minimum angle of total reflection is limited. When a polarization beam splitter is used to guide light, limitations are imposed due to dependency of the reflectivity of S waves on the incident angle. From these facts, the illumination luminous flux incident on the light modulation element is desirably close to a collimated luminous flux.
In addition, when a transmission type liquid crystal display panel is used as the light modulation element to modulate light of tree primary colors of red, green, and blue, the modulated light components are then combined by a dichroic mirror or dichroic prism. In this case, as the modulated light is less similar to a collimated luminous flux, the cut wavelength in a reflection/transmission wavelength region of a dichroic film is changed to produce turbidity of colors or variations in color reproducibility depending on the position of a projected image.
When twisted nematic liquid crystal (TNLC) is used as the light modulation element, whether it is of a transmission type or a reflection type, as the incident angle of an illumination luminous flux on the liquid crystal display panel is more inclined with respect to the normal to the panel, and more inclined with respect to the rubbing direction of liquid crystal molecules in the liquid crystal display panel plane, a larger deviation occurs from 0 or π which is an ideal phase difference of a wave provided by transmission through the liquid crystal display panel. Therefore, contrast in light modulation is reduced.